In bearing or supporting an engine mounted on an automobile in a vibration-absorbing manner, because of the fact that the number of rotations per minute of the engine per se changes over a wide range, a vibration-absorbing mounting device is required that is capable of fulfilling two requirements, namely, the damping rate relative to large-amplitude, low-frequency oscillations which are generated upon running at a low speed be large; and the vibration insulation capacity against high frequency oscillations occurring at high speed be large.
Vibration-absorbing mounting devices of this kind which are constituted of rubber or an air spring having a high damping material cannot retain effective vibration insulation performance over a wide range of oscillations since enhancing damping capacity against low frequency oscillations makes dynamic spring characteristics large and conversely, improving dynamic spring characteristics leads to the result that the damping capacity against low frequency oscillations is not exhibited.
In order to alleviate such drawbacks or disadvantages as described above, extensive research and development has been conducted pursuing vibration-absorbing mounting devices capable of exhibiting substantial, good vibration-absorbing properties against both high and low frequency oscillations. Just all-round vibration-absorbing mounting devices of various shapes have heretofore been proposed. Among them, for instance, there is known a vibration absorbing mounting devices with fluid damping with which the damping function against oscillations can be shared by a sealed fluid and the vibration function can be shared by a rubber layer.